A thin film transistor (hereinafter referred to as a “TFT”) array substrate that structures an active matrix driven type liquid crystal display panel is provided with a TFT as a switching element per pixel, which is the smallest unit of an image.
For example, a bottom-gate type TFT includes a gate electrode that is arranged on an insulating substrate, a gate insulating film that is arranged so as to cover the gate electrode, a semiconductor layer that is arranged to be island-shaped on the gate insulating film so as to overlap the gate electrode, and a source electrode and a drain electrode that are arranged on the semiconductor layer so as to oppose to each other.
Here, in connection with the liquid crystal display panel, if any conductive foreign object or film residue is interposed between the source electrode and the drain electrode in any TFT provided per pixel, a short-circuit may possibly be established at the source electrode and the drain electrode, making it impossible for the pixel to operate correctly. Accordingly, there has been proposed a TFT array substrate that is provided with a plurality of TFTs per pixel (see PATENT DOCUMENTS 1 and 2, for example).
For example, PATENT DOCUMENT 1 discloses, in FIGS. 2 to 4, an active matrix substrate that includes source lines, pixel electrodes, first TFTs that switch the electrical connection between them, and second TFTs as spares. The second TFTs each include a semiconductor film at which a source electrode and a drain electrode are formed, and a gate electrode arranged at the semiconductor film having a gate insulating film interposed therebetween. The source lines are each arranged relative to the semiconductor film of corresponding one of the second TFTs having an interlayer insulating film greater than the gate insulating film in thickness interposed therebetween. The source lines are each configured to be capable of being electrically connected to the source electrode by formation of a contact hole at the interlayer insulating film, in a situation where corresponding one of the first TFTs fails. The second TFT can carry out switching of the electrical connection between the source line and the pixel electrode.